Such a hydraulic arrangement can be used, for example, in a reverse osmosis system. In such a reverse osmosis system polluted or salted water is pumped under high pressure through a membrane. Part of the water penetrates the membrane and can be gained as purified water. The remaining part of the water which is still under a relatively high pressure, has to be wasted. However, in order not to lose too much energy, the pressure of this part of the water should be recovered. To this end a pressure exchanger is used transferring the pressure of the wasted water at least partially to fresh water. Since some pressure losses are unavoidable, a booster pump is used to bring the fresh water to the pressure level needed for reverse osmosis.